As the technology of human reproduction becomes ever-more sophisticated, new ethical issues come to the fore - even as some are resolved.
The latest development involves the first successful pregnancy in the United States using human eggs that had been frozen. If the technique used by the doctors in Atlanta can be regularly replicated - and they predict it can - then women's reproductive options can be greatly expanded.
Girls and women facing fertility-threatening cancer treatment will be able to freeze healthy eggs in "egg banks," just as men are able to do with sperm. Women heading toward menopause who believe they may want to conceive a child later may save eggs for future use.
But as with any technological innovations bearing on human life, new moral questions are raised. "The issue is, once we have the capacity to do something, what kind of immoral uses can we put it to?" asks Gail Povar, chairman of the medical ethics committee of George Washington University Hospital here.
Medical ethicists are also concerned that some doctors will routinely encourage young women to freeze their eggs - especially those who think they may want to conceive later in life, when their eggs will be less viable - without appropriate concern for the difficulty involved.
While saving sperm is easy, harvesting a woman's eggs involves surgery, sonograms, and, frequently, stimulation of the ovaries to make sure enough eggs are produced to make the procedure worthwhile. In addition, because eggs are more fragile than sperm, researchers are concerned that the freezing and thawing process poses a greater risk of chromosomal abnormalities with thawed eggs.
Because frozen and thawed eggs have produced only a few successful pregnancies in the world - others have taken place in Australia and Hong Kong - it isn't known if the rate of abnormalities will be higher than with natural pregnancies.
"We won't know until there's been a hundred outcomes at least," says Joe Massey, one of the Atlanta doctors who worked on the recent case of healthy twin boys born to an infertile woman who used donated frozen eggs.
IF this is a viable option, then it could provide a way to avoid the thorny issue of "ownership" of frozen embryos, because it will apparently give couples the option of freezing sperm and eggs separately. Decisions about destroying frozen sperm or eggs will rest with their sole donors, rather than with two people who may come to disagree about the embryos' fate.
But on another front, society has solved none of the legal issues surrounding sperm storage yet, so it follows that the same issues would come up over egg storage, says George Annas, a bioethicist at Boston University's School of Public Health.
If a person stores sperm or eggs for personal use during his or her lifetime, then the likelihood of legal problems is small, he says. But if one stores material for use by someone else, a range of issues comes up: If the owner dies, who decides the fate of the sperm or eggs? If donated sperm or eggs are used to produce a child, does that child have a right to know the donor's identity?
"The best option is to destroy eggs and sperm upon the death of the donor, but there are no laws governing any of this," says Mr. Annas. "It's a wild frontier out there."
Intelligently run sperm banks, he says, make donors decide these issues up front.
On a more fundamental level, the advent of the use of frozen human eggs in reproduction will only intensify religious debate about whether medical science should be interfering at all in conception. In some faiths, medical intervention is viewed as a subversion of natural law.
In the medical world, though, advances in technology represent a way to help infertile couples achieve a long-held dream. The use of frozen eggs means that women who in the past would have had to use another woman's eggs now have the option of using their own eggs (with advance arrangements), though it is unclear how many years frozen eggs remain viable. In the Atlanta case, the eggs had been frozen for 25 months.
In cases where donated eggs are needed, the ability to use frozen eggs could simplify the donation process, as well as reduce its cost. Currently, with donated eggs, the reproductive cycles of the two women involved have to be coordinated through artificial manipulation. And because donated eggs couldn't be frozen, many were wasted.
If women's biological time clocks have indeed been shattered, then a future of post-menopausal mothers beckons. Already, older women are using donated eggs to have babies, raising debate about what's appropriate for themselves and their children. But in a world where men routinely conceive children well into old age, many observers question why women shouldn't have the same option.
"How much societal control over when and how people become parents are we willing to accept?" asks Dr. Povar of George Washington University.
"There are plenty of very unacceptable parents between the ages of 18 and 40 who have babies because they're biologically capable," says Povar. "So why should we allow age alone to be the criterion?"